Melt the butter in medium bowl and set aside for later use.
In a standing mixer beat the eggs and sugar on high speed for 10 minutes. The mixture must be thick, pale, almost white. Add in the lemon zest, strawberry purée (or red food colouring) and vanilla extract. Mix until combined.
Sift a flour, baking powder, and salt together in a small bowl and mix it together. Using a spatula gently fold half of the flour mixture into egg mixture. Once incorporated, fold in the other half of the flour mix.
Pour ⅓ of the batter into the melted butter and gently fold in with spatula or wooden spoon. It will take a while to perfectly incorporate it. But take your time and incorporate well. Now, gently pour back the mixture with butter on the side of the bowl with the rest of the batter. Fold in delicately with spatula.
Cover the batter with food wrap and chill in the refrigerator for at least one hour. You can let it chill overnight.
Preheat the oven on 190 C/ 375 F, middle rack and prepare madeleine pan by brushing it with butter and powder with flour.
Spoon the batter into the centre of each opening and gently spread (flatten) with small spatula.
Bake for 8-11 minutes. The madeleines are done when the top is lightly golden, you can also try with your finger to push gently on and if it springs back, it's done. Invert the pan onto the counter and transfer the madeleines onto a wire rack to cool them down.
Dust with confectioners’ sugar, before serving. Enjoy it as soon as you can, otherwise madeleines tend to become spongy after one day of baking.